: Growth factors (GFs) play an important role in development and growth of mammary and endometrial cancer. Some evidence suggests that GFs and protein kinase (PK) inducers activate estrogen-dependent gene expression via estrogen receptor (ER)-dependent and -independent pathways. Moreover, preliminary studies show that 2,3,7,8-tetrchlorodibenzo-p-dioxin (TCDD), a prototypical aryl hydrocarbon receptor (AhR) agonist, inhibits GF/PK-ER crosstalk in MCF-7 human breast cancer cells. Therefore, Dr. Safe hypothesizes that (a) GF/PK-mediated induction of cathepsin D and c-fos protooncogene expression and cell growth involves both ER-dependent and -independent pathways and (b) AhR agonists (an important class of environmental contaminants) modulate GF/PK-ER crosstalk and can be used to probe the mechanism of interaction between the two signaling pathways. This proposed study will utilize Ah-responsive ER-positive MCF-7 and ER-negative MDA-MB-468 breast cancer cells, and selected AhR agonists. The following specific aims will test the validity of our hypothesis: Aim 1: The effects of GFs and PK inducers on cathepsin D gene expression will be thoroughly investigated in different cell types using wild-type and mutant ER expression plasmids. This Aim will take advantage of ongoing studies which have identified three distinct estrogen-responsive promoter regions containing Sp1/ERE(1/2), Sp1 and imperfect palindromic ERE motifs (ES1, ES2 and ES3, respectively). Aim 2: This Aim will utilize c-fos protooncogene and related promoter- reporter constructs as a second model for investigating GF/PK-ER crosstalk and the role of ER-dependent and -independent pathways of gene regulation. Previous studies have identified functional inhibitory dioxin responsive elements (iDREs) within the c-fos protooncogene and cathepsin D gene promoters, which are required for AhR-mediated antiestrogenicity. Aim 3 will determine the mechanism of inhibition of GF-induced responses by AhR agonists. Aim 4 will focus on GF-induced cell cycle enzymes and targeted inhibition by AhR agonists. The proposed studies will determine the mechanism of GF/PK-induced transactivation of c-fos and cathepsin D and delineate both ER-dependent and - independent pathways. The effects of AhR agonists will determine impacts of important dietary/environmental endocrine disruptors on these coupled endocrine pathways, which play important roles in development of hormone-dependent cancers.